Sterilization of carboys can be done using commercial brewing sterilizing chemicals, bleach and water (make sure you rinse well!!), or boiling water. Boiling water for sterilizing is the safest as far as the brewers I know concur. But damn, that stuff is hot, so I have been known to use bleach and water, let the mix sit for a few hours, scrub with a carboy cleaner, and rinse 3-4 times very well with water.